The differences between LSAW steel pipe and SSAW steel pipe are as follows:


1. Welding technology involves: consistent spiral welded pipe and longitudinal welding, straight seam steel pipe will inevitably have a large number of T-type welding, so the possibility of welding defects is greatly improved, welding residual T-weld stress is large, weld metal is often in a three-dimensional stress state, increasing the possibility of cracks. In addition, according to the requirements of submerged arc technology, each weld should have arc and extinction, but in each longitudinal weld ring, it can not meet the conditions, and there may be more weld defects in extinction.


2. When the pipeline is subjected to pressure, two principal stresses, i.e. radial and axial stresses, are usually generated on the wall. The weld is stitched into stress delta, in which the spiral angle of the weld is included.


3. The helical angle of spiral welded pipe is generally the synthetic helical welding stress is the principal stress. Under the same operating pressure, the helical tube with the same diameter and longitudinal wall thickness can be reduced.


4. Static water impact strength: The measured and theoretical values of yield pressure and blasting pressure are basically identical with the longitudinal values, and the deviation is close through the relevant comparative tests. However, the yield stress or blasting pressure of the spiral tube is not lower than the longitudinal direction. The blasting test also shows that the deformation rate of the spiral steel hoop blasting hole is obviously greater than that of the longitudinal direction. It is proved that the plastic deformation ratio of spiral pipe is longitudinal, and the blasting opening is generally confined to a pitch, which has a strong restraint effect on the expansion gap of spiral weld.


5. Toughness and fatigue strength: Pipeline development trend is large diameter, high strength. With the increase of pipe diameter, the steel grade increases, which leads to the trend of stable expansion at the tip of ductile fracture. The spiral pipe has the same level as the longitudinal one, but the spiral pipe has higher impact toughness.


6. Because of the change of the output of transmission line: In practice, the pipeline is subjected to random alternating action load. Understanding the low cycle fatigue strength of steel and judging the service life of pipeline are of great significance.


7. According to the measurement results, the fatigue strength of seamless spiral steel and ERW pipe have the same test data and the distribution and resistance of seamless pipe are in the same region, while the longitudinal submerged arc is higher than the average value.